Television receiver



Dec. 31, 1940. K. SCHLESINGER TELEVISION RECEIVER Filed Feb. 9, 1955 Jnvenfor:

Wm WM Patented Dec. 31, 1940 PATENT. ori ice TELEVISION l I I Kurt Schlesinger, Berlin, ,centan 'gssi n poration of New York Application February 9, 193 5,;SerialNo. 5,872

In Germany February 12, 19341 7 mesne assignments, to Loewe Rladio,.lnc., a cor- 2 Claims. (01,1 8.43

In the television methods known per se, in which frame and line synchronizing impulses are transmitted as modulations of the same carrier wave with the image signals and exceed the latter in amplitude the following difliculties occur in practice: I i

It is assumed that a transmitter possesses the modulation curve shown in Fig. 1. Above the time axis T there is shown the course of the modulation potential, the potential ll belonging to a grey image point. The image current modulation' extends between the maximum and minimum values I and .2, which correspond with light white and deep black in the picture. The curve during a line is, for the sake of comprehension, assumed to be a sine-wave 3. After termination of a line there is transmitted a line impulse 4, the sign of which is negative, i. e., is assumed to correspond with a black margin to the picture. Thisline impulse may extend to an ordinate 5, and it is assumed that the same extends from the black value ofthe image modulation 2 to exactly the same extent into negative as the white value I extends into positive; To make the positionmore clear it is assumed that a very white image'point is modulated with 5 volts positive potential, and a deep black image point with -5 volts, so that in view of the above remarks the line impulse requires to be passed to the transmitter with -15 volts. I

It will be quite obvious that a difference in amplitude-of this nature between the line impulses and the black in the image means nothing else than that a large proportion of the transmission energy is not utilised for the transmission, or "in other words that the transmitter cannot be sufficiently modulated with the actualimage contents 3, viz., at the most to the extent of 50%. A considerable improvement would accordingly be obtained, if the diflerence in amplitude between the peak value of the line impulse and the peak value of the image impulse could be reduced. From a practical point of view, however, there is a limit in this direction involved by the unavoidable fluctuations in the transmission bythe natural noisesof the reception, by fluctuations in the total degree of amplification of the receiver and also by the limited separating efficiency of the amplitude filter. v

In any case for reliable television operation an amplitude ratio of approximately 1:1 is shown in Fig. 1.

The invention consists in the use of non-linear amplifiers in the receiver furnishing to the amplitude filter signals with large difference in potential according to Fig. 1,. whereas the tran'smitter is modulated at a muchlower degree and is accordingly better utilized.

7 Figs. 1, 2 and 3 are explanatory diagrams, While i s 5 Fig. 4 is aspecific embodiment of applicants invention.

Fig. 2 servesto make'the matter more clear. In the same there is. shown .a curved amplifier tube characteristic 6. If arr-amplifier of this 10 nature is'furnished' with a voltage-time curve according toFig. 1, there is obtained a distortion..' To simplify matters the curved characteristic 6 isreplaced by two straight lines 6' and 6",. and there is obtained an image modulation 15 3 and a line impulse 4" with a 'much smaller difference in amplitude than in the primary curve. Apparently, therefore, with a characteristic in the form of 6 thereis accomplished exactly'the opposite to thatwhich was sought to 20 be attained. A"characteristic of this nature belongs. in practice to a negatively biassed anode bend rectifier without gridcurrent. The same may be referred to as a convex characteristic.

In Fig. 3 there is shown the'counterpart there- 25 to, via, a concave characteristic. The characteris'tic itself is designated 1', and'is replaced by thetwo tangents 'I' and l".? An amplifier of this nature produces the amplitude diagram 3" and l". In this arrangement the difference in amplitude between line impulse and contents of the image is evidently considerably increased, i. e., the desired variation in scale, practically attained.

. In the case of transmitters with modulation reverse to that of Fig. 1, in which, therefore, 35 the synchronisation signals exceed in positive directionthe image modulation, as have already be'comeknown in practice a reversal of theseconditionstakesplace and a characteristic accord ing toFig. 2 has to be used. l

The practical execution of. this method is ex- 40 plained by Fig.4. I Thereisassumed to be a television transmitten which operates with negative line impulses and possesses merely a small excess of amplitude between synchronising signal 45 and image signal, Le, a transmitter which is well utilised and is modulated with the image current to the extent of approximately and with the synchronising signals to the extent of approximately The receiver is a super- 50 het, which receives with an aerial 8, converts by means" ofa. local oscillator 9 the ultra-short wave picked up into a comparatively long intermediate wave, and amplifiesthe latter in an intermediate-frequency amplifier I0. Up to now a 55 total characteristic is assumed which is strictly linear. Linear operation is abo assumed to exist in the rectifier II, so that the signalling potentials passed to the intensity control electrodes of the television tube I2 are correctly proportioned to the transmitter modulation amplitudes, The amplitude filter, which is intended to separate the synchronising signals from the image signals, is a gas-filled diode l3 with hot cathode Hand laxation oscillator to be synchronised. According to the invention there is provided between t the detector output l6 and this filter tube 13 an amplifying tube II with suitably curved (concave) characteristic, which causes an amplifying variation in scale in favour of the synchronising signal, in accordance with Fig. 3. A'char-j acteristic of this nature may be given to the tube by utilising the grid current. For this purpose the control grid l8 of the tube I1 is not furnished with a negative bias, but is connectedto the cathode in direct fashion through the medium of a leakage resistance [9. A grid condenser 20 requires. to be so small that the same together witth the resistance l9 possesses a-time constant of approximately the time occupied by the transmission of one image point. It isthen, and only then, that the characteristic of thetube I1 becomes concave even in respect of the shortest impulses 4. Otherwise there results owing to too slow discharge ofthe grid ,charge'a'frequency-dependency of the'efiective transmission characteristic of 18 in'the form of a weakening of the high frequencies. Since the synchronising signals which are concerned endureonly for a few image points, i. e., belong to the shortest signals which are transmittted at all, values of 20:25 mmf. and l9=10,000 ohms with a time constant of a few microseconds are necessary and sufii-' in phase at maximum frequency; i. e., amount to approximately 1000 ohms.

In' the case of a positively modulated trans- 5 mitter there is imparted a negative bias, to the control grid so that the valve is operating like an anode bend rectifier, and the considerations with regard to the inertia of the grid circuit do not apply.

1) It is possible to unite structurally the two tubes I1 and 13. For this'purpose it is of course necessaryto remove the gas-filling of [3, and the loss in separating efliciency thus incurred must be counter-balanced by a but slight amplification in 5 the tube 11. For this purpose a somewhat larger anode resistance 2| of approximately 5000 ohms is necessary and sufficient. The scale-varying element Il may be replaced by imparting to the detector II a concave characteristimor to one of the final tubesof the carrier frequency amplifier ID, by means of a grid-current effect like to valve H in the drawing. The amplitude scale of the. image signals is then somewhat falsified.

I claim:

1. A television system adapted to receive a radio frequency carrier modulated by a series of picture and synchronizing signals where the synchronizing signals are transmitted at substantial- =ly maximum carrier intensity and where the anode l5. Its cathode is connected to the re- A a r w stantially 80% maximum carrier intensity comprising means to receive and amplify the received carrier, means to demodulate the carrier to produce detected picture and synchronizing signals With the ratio of the strongest picture signals to the synchronizing signals being of the order of approximately 4 to 5, means for applying the detected picture and synchronizing signals to a picture producing device, an electron discharge tube having a cathode, a control electrode and an anode, a resistance connecting the control electrode to the cathode of the tube, means including a relatively low capacity condenser connected to said control electrode for applying the detected. picture and synchronizing signals to the control electrode,'the values of the condenser and resistance being such that their time constant is of the order of the time required to transmit one picture element, the value of the resistance being relatively low whereby a non-linear concave control electrode potential ariode current characteristic will result, means including a load circuit for maintaining said anode positive with respect to said cathode whereby picture and syn-' chronizing' signals will appear at theanod'ein distorted form with respect to the applied sig-. nals, the distortion caused by the non-linear characteristic resulting in an attenuation of the picture signals and a change in the ratio of the pictureto synchronizing signals to (at least the order of one to one whereby a separation of the picture signals from the synchronizing signals" may bemore readily accomplished, and means for separating the'synchronizing signals fromthe picture signals for synchronizing purposes. 2. A'television system adapted to receivea radio frequency carrier modulated by a series of picture and synchronizing. signals where the syn chronizing signals are transmitted at substan-; tially maximum carrier intensity and where the picture signals are transmitted at values within: the ran'ge'between substantiallyzero to substantially 80% maximum: carrier intensity comprising means to receive the received-carrier, 'means todemodulate the carrier to produce detected picture and synchronizing signals withthe ratio of the strongest picturesignals to the synchro nizing signals being of the order of approximately- 4 to 5,an electron discharge tube having a cath ode, a control grid andan anode, a resistance? connecting the control grid to the cathode of the tube, means including a relatively low, capacity condenser connected to said control electrode for applying the detected picture and synchroniz'-' ing' signals'to the control'grid, the values of the condenser and resistance being such that their time constant is of the order of from two to five micro-seconds, the'value of the resistance being relatively low whereby grid current may; flow and whereby a non-linear concave gridpoe tential-anode current characteristic will result; means including a loadcircuit for maintaining said anode positive with respect to said cathode" whereby picture and synchronizing signals will: appear at the anode in distorted form with ,re' spect to the applied signals, the distortion caused by the non-linear characteristic resulting in an:- attenuation of the picture signals and a change in the ratio of the strongest picture signals to the synchronizing signals from approximately 4 to 5 at least the order of unity. I KURT SCHLESING Eli- 

